Method and apparatus for gas turbine dry low nox combustor corrected parameter control

ABSTRACT

A method for controlling a combustor of an engine, the combustor having a fuel to oxidant ratio, the fuel to oxidant ratio being defined as a ratio of an amount of fuel supplied to the combustor divided by an amount of oxygen in an oxidant stream supplied to the combustor includes controlling the fuel to oxidant ratio of the combustor as a function of the amount of oxygen in the oxidant stream.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/906,689, filed on Mar. 2, 2005, the disclosure of which isherein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This application relates generally to combustors and, more particularly,to gas turbine combustors.

A present thrust of gas turbine engine technology seeks to attainreduced emissions of nitrogen (NOx) and hydrocarbon compounds.Techniques for accomplishing such reduced emissions often result inreduced thermodynamic efficiency or substantially increased capitalcosts.

NOx compounds are produced by a reaction of the nitrogen in an oxidantat elevated temperatures conventionally found in the combustors of a gasturbine engine. NOx formation can be reduced by reducing the maximumflame temperature in the combustor. Injection of steam into thecombustor reduces the maximum flame temperature in the combustor at acost in thermodynamic efficiency. Penalties must also be paid in wateruse, including water treatment capital outlay and operating costs. Theamount of steam injection, and its associated cost, rises with theamount of NOx reduction desired. Some states and foreign countries haveannounced targets for NOx reduction that infer such large quantities ofsteam that this solution appears less desirable for future systems.

Reduction or elimination of hydrocarbon emissions is also attainable byensuring complete combustion of the fuel in the combustor. Completecombustion requires a lean fuel-oxidant mixture. As the fuel-oxidantmixture is made leaner, a point is reached at which combustion can nolonger be supported. Thus, significant research has been conducted toreduce the maximum flame temperature, while still permitting efficientoperation of the combustor.

Dry low NOx combustion, which limits NOx formation by lowering flametemperatures through fuel/oxidant optimization, has been developed. Drylow-NOx combustors control fuel and oxidant mixing to create larger andmore branched flames, reduce peak flame temperatures, and lower theamount of NO_(x) formed. In principle, there are three stages in aconventional dry low-NO_(x) combustor: combustion, reduction, andburnout. In the initial stage, combustion occurs in a fuel-rich,oxygen-deficient zone where the NO_(x) is formed. A reducing atmospherefollows, where hydrocarbons are formed and react with the already formedNO_(x). In the third stage, internal oxidant staging completes thecombustion.

While dry low NOx combustion in a gas turbine has produced gains in theeffort to reduce NOx emissions, dry low NOx combustion is sensitive tochanges in oxygen content in the combustor oxidant. Oxidant supplied tothe combustor is usually composed of ambient air brought in through acompressor that has varying oxygen content due to dilution with ambientwater vapor and possibly additional water vapor from an evaporativecooler or other device that cools inlet air through evaporation ofwater. In addition, other diluents (such as steam, nitrogen or liquidwater) are occasionally added to the oxidant before or during thecombustion process. Thus, it is desirable to determine the oxygencontent in the total oxidant.

BRIEF DESCRIPTION OF THE INVENTION

Exemplary embodiments of the invention include a method for controllinga combustor of an engine, the combustor having a fuel to oxidant ratio,the fuel to oxidant ratio being defined as a ratio of an amount of fuelsupplied to the combustor divided by an amount of oxygen in an oxidantstream supplied to the combustor. The method includes controlling thefuel to oxidant ratio of the combustor as a function of the amount ofoxygen in the oxidant stream.

Further exemplary embodiments of the invention include a gas turbineengine having an oxidant stream and a fuel supply. The gas turbineengine includes a turbine, a compressor, a combustor, an oxygen sensor,a fuel system and a controller. The compressor is in mechanicalcommunication with the turbine. The combustor is in fluid communicationwith both the turbine and the compressor. The combustor receiving theoxidant stream and the fuel supply. The oxygen sensor adapted to producean oxygen level signal responsive to an amount of oxygen in the oxidantstream. The fuel system provides the fuel supply to the combustor. Thecontroller is in electrical communication with the oxygen sensor, thecompressor and the fuel supply system.

The above, and other objects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention will be more apparent fromthe following description in view of the drawing that shows:

FIG. 1 is a schematic diagram of a gas turbine engine using oxygencontent to control a combustor according to an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary embodiment of a gas turbine engine. The gasturbine engine includes a combustor 10. Combustor 10 bums a fuel-oxidantmixture to produce a flow of gas 12 which is hot and energetic. The flowof gas 12 from the combustor 10 then travels to a turbine 14. Theturbine 14 includes an assembly of turbine blades (not shown). The flowof gas 12 imparts energy on the assembly of turbine blades causing theassembly of turbine blades to rotate. The assembly of turbine blades iscoupled to a shaft 16. The shaft 16 rotates in response to a rotation ofthe assembly of turbine blades. The shaft 16 is then used to power acompressor 18. The shaft 16 can optionally provide a power output 17 toa different output device (not shown), such as, for example, anelectrical generator. The compressor 18 takes in an oxidant stream 20. Aflow of the oxidant stream 20 is controllable by a controller 22.Controller 22 uses an airflow adjustment signal 24 to control a geometryof an air inlet device (not shown) of the compressor 18. The oxidantstream 20 is compressed in the compressor 18. Following compression ofthe oxidant stream 20 a compressed oxidant stream 23 is fed into thecombustor 10. The compressed oxidant stream 23 from the compressor 18 ismixed with a fuel flow 26 from a fuel supply system 28 to form thefuel-oxidant mixture inside the combustor 10. The fuel-oxidant mixturethen undergoes a burning process in the combustor 10.

The oxidant stream 20 input into the compressor 18 includes a pluralityof components. The plurality of components include a dry air componentand a water vapor component. The water vapor component is due to localambient conditions as well as to evaporation of additional water forcooling purposes into the compressor inlet flow. Atmospheric dry aircontains a nitrogen component, an oxygen component, an argon component,a carbon dioxide component, and additional trace components of very lowconcentration such that they may be ignored. Each dry air componentexists in a specific proportion relative to the overall quantity ofatmospheric dry air. The oxidant stream 20 includes the atmospheric dryair and water vapor. When the oxidant stream 20 is compressed in thecompressor 18, it is fed into the combustor 10 as the compressed oxidantstream 23. The compressed oxidant stream 23 may include components otherthan atmospheric air. Thus, a concentration of oxygen in atmospheric airmay not be same as a concentration of oxygen in the compressed oxidantstream 23. Since the amount of oxygen in the compressed oxidant stream23 directly impacts the burning process in the combustor 10, it isimportant to know the amount of oxygen in the compressed oxidant stream23. Oxygen in the compressed oxidant stream 23 combines with the fuelfrom the fuel flow 26 to burn in the combustor 10. A ratio of an amountof fuel supplied to the combustor 10 divided by an amount of oxygen inthe compressed oxidant stream 23 supplied to the combustor 10 is calleda fuel to oxidant ratio. Controlling the fuel to oxidant ratio resultsin control of the burning process. For example, a lower fuel to oxidantratio results in a more complete combustion of the fuel due to anabundance of oxygen.

The controller 22 receives an input regarding a combustor parameter andprovides a control of the combustor 10 responsive to the combustorparameter to enhance the fuel to oxidant ratio. The combustor parameterincludes, but is not limited to, a power level signal 30, an atmosphericpressure signal 32, a turbine inlet pressure signal 34, a turbineexhaust pressure signal 36, an oxygen level signal 38, a turbine inlettemperature signal 42, an inlet geometry signal 45 and a fuel flowsignal 46. The inlet geometry signal 45 is sent from the combustor 10 tothe controller 22. The inlet geometry signal 45 informs the controller22 of the geometry of the air inlet device (not shown) of the compressor18. The fuel flow signal 46 informs the controller of the fuel flow 26to the combustor 10. In an exemplary embodiment, the controller 22receives a plurality of combustor parameters from among those listedabove to control the combustor 10 to enhance the fuel to oxidant ratio.

A premise of dry low NOx turbines is to reduce a flame temperaturethrough an optimization of the fuel to oxidant ratio. The optimizationof fuel to oxidant ratio requires a measurement of the amount of oxygenin the compressed oxidant stream 23 and measurement of the fuel flow 26to the combustor 10 in conjunction with a control of either or both ofthe amount of oxygen in the compressed oxidant stream 23 and the fuelflow 26. An oxygen sensor 40 measures the amount of oxygen in thecompressed oxidant stream 23 and produces the oxygen level signal 38responsive to the amount of oxygen in the compressed oxidant stream 23.In an exemplary embodiment, the oxygen sensor 40 is a GE O2X1 oxygenanalyzer, however, the use of other oxygen sensors is also contemplated.Additionally, oxygen level will vary if a substance other thanatmospheric air is entering the compressor 18. Regardless of thesubstance entering the compressor 18, the oxygen sensor 40 is capable ofproducing the oxygen level signal 38, which the controller 22 correctsfor atmospheric conditions to allow control of the fuel to oxidantratio.

The oxygen level signal 38 is corrected for current atmosphericconditions by the controller 22. A reference oxygen level is measured ona reference day with reference parameters. The reference parametersinclude a reference turbine inlet pressure, a reference turbine exhausttemperature, and a reference atmospheric pressure. The controller 22corrects the oxygen level signal 38 by providing an adjustment based oncurrent conditions as indicated by the atmospheric pressure signal 32,the turbine inlet pressure signal 34, and the turbine exhaust pressuresignal 36. The result of the adjustment is a corrected oxygen level. Thecorrected oxygen level indicates the amount of oxygen in the compressedoxidant stream 23.

An exemplary embodiment of the present invention employs a digitalintegrated system control General Electric Mark VI controller 22 tocontrol the fuel flow 26 and/or the compressed oxidant stream 23 intothe combustor 10 to enhance the fuel to oxidant ratio, thereby providingdecreased NOx production with the greatest gas turbine engineefficiency. Although the controller 22 is described as the integratedsystem control General Electric Mark VI, the use of any other suitablecontroller is envisioned. Optimization of the fuel to oxidant ratio is afunction of the power level of the gas turbine engine and the amount ofoxygen available for combustion. In other words, there is a uniqueenhanced fuel to oxidant ratio for each power level of the gas turbineengine. The power level signal 30 is responsive to the power level ofthe gas turbine engine. The corrected oxygen level, derived from currentatmospheric conditions and the oxygen level signal 38 indicates theamount of oxygen in the compressed oxidant stream 23. The controller 22references power level signal 30 to access, from a data table within thecontroller 22, the enhanced fuel to oxidant ratio for a power levelmatching the power level signal 30. The turbine inlet temperature signal42 is used as an indication of the fuel to oxidant ratio for a givenpower level of the gas turbine engine. Thus, the controller 22 comparesthe turbine inlet temperature signal 42 to a desired turbine inlettemperature for the power level corresponding to the power level signal30. Matching the turbine inlet temperature signal 42 to the desiredturbine inlet temperature for the power level corresponding to the powerlevel signal 30 achieves the enhanced fuel to oxidant ratio. Atemperature sensor 44 disposed at an inlet of the turbine 14 producesthe turbine inlet temperature signal 42.

As stated above, matching the turbine inlet temperature signal 42 to thedesired turbine inlet temperature for the power level corresponding tothe power level signal 30 achieves the enhanced fuel to oxidant ratio.Thus, the controller 22 determines, based on the corrected oxygen leveland the turbine inlet temperature signal 42, whether to adjust the fuelflow 26 or the compressed oxidant stream 23 to achieve the enhanced fuelto oxidant ratio for the power level matching the power level signal 30.A fuel flow adjustment signal 48 is used to adjust the fuel flow 26 tothe combustor 10. The airflow adjustment signal 24 is used to adjust thegeometry of the air inlet device (not shown) of the compressor 18,thereby adjusting the compressed oxidant stream 23. Thus, the controller22 sustains a lean fuel-air mixture to reduce NOx formation, butprevents such phenomena as a flameout.

Controller 22 continuously receives current conditions to permitcalculation of the corrected oxygen level. Controller 22 alsocontinuously receives power level signal 30 to determine the enhancedfuel to oxidant ratio for the power level matching the power levelsignal 30 as indicated by the desired turbine inlet temperature. Theenhanced fuel to oxidant ratio is achieved by continuously adjustingeither or both of the fuel flow 26 or the compressed oxidant stream 23to the combustor 10 as necessary to control the corrected oxygen leveland turbine inlet temperature signal 42.

In addition, while the invention has been described with reference toexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another.

1. A gas turbine engine having an oxidant stream and a fuel supplycomprising: a turbine; a compressor in mechanical communication withsaid turbine; a combustor in fluid communication with both said turbineand said compressor, said combustor receiving the oxidant stream and thefuel supply; an oxygen sensor, said oxygen sensor adapted to produce anoxygen level signal responsive to an amount of oxygen in the oxidantstream; a fuel system, said fuel system provides the fuel supply to saidcombustor; and a controller in electrical communication with said oxygensensor, said compressor and said fuel supply system.
 2. The gas turbineengine of claim 1, wherein said controller is configured to control ofat least one of the fuel supply and the oxidant stream.
 3. The gasturbine engine of claim 1, wherein said controller is responsive to saidoxygen level signal.
 4. The gas turbine engine of claim 3, wherein saidcontroller corrects said oxygen level signal based on a currentatmospheric condition that differs from a reference atmosphericcondition.
 5. The gas turbine engine of claim 4, wherein said currentatmospheric condition and said reference atmospheric condition aremeasured with respect to at least one of: a turbine inlet pressure; aturbine exhaust pressure; and an atmospheric pressure.
 6. The gasturbine engine of claim 1, wherein said controller is configured toachieve a fuel to oxidant ratio that is an enhanced fuel to oxidantratio, said fuel to oxidant ratio being defined as a ratio of an amountof fuel supplied to said combustor divided by said amount of oxygen inthe oxidant stream to said combustor.
 7. The gas turbine engine of claim6, wherein said enhanced fuel to oxidant ratio is determined based on apower level of the gas turbine engine.
 8. The gas turbine engine ofclaim 6, wherein said fuel to oxidant ratio is indicated at a givenpower level by a turbine inlet temperature.
 9. The gas turbine engine ofclaim 6, wherein said enhanced fuel to oxidant ratio is indicated by adesired turbine outlet temperature for a given power level.